Pluripotent stem cells, including embryonic stem cells and induced pluripotent stem cells are capable of differentiating into all somatic cells of the body. The differentiated cells have potential for major advances in human health. For example, the cells can be used as targets for studying the effects of drugs on specific cells, as models of human disease that can be studied in vitro, and/or to provide a potentially limitless supply for cell therapies for diseases. Many problems stand in the way of achieving the envisioned potential of stem cells. Both embryonic stem cells and induced pluripotent stem cells are difficult to grow and culture while keeping them in the undifferentiated state. In addition, the factors that dictate stem differentiation are not well understood and control of differentiation of stem cells into specific cell lineages and in sufficient quantities remains an obstacle. Accordingly, improved articles and methods for stem cell differentiation are needed.